40 lines
935 B
Text
40 lines
935 B
Text
/-
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Copyright (c) 2019 Microsoft Corporation. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Authors: Daniel Selsam
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Simple queue implemented using two lists.
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Note: this is only a temporary placeholder.
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-/
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namespace Std
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universes u v w
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structure Queue (α : Type u) :=
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(eList dList : List α := [])
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namespace Queue
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variable {α : Type u}
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def empty : Queue α :=
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{ eList := [], dList := [] }
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def isEmpty (q : Queue α) : Bool :=
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q.dList.isEmpty && q.eList.isEmpty
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def enqueue (v : α) (q : Queue α) : Queue α :=
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{ q with eList := v::q.eList }
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def enqueueAll (vs : List α) (q : Queue α) : Queue α :=
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{ q with eList := vs ++ q.eList }
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def dequeue? (q : Queue α) : Option (α × Queue α) :=
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match q.dList with
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| d::ds => some (d, { q with dList := ds })
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| [] =>
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match q.eList.reverse with
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| [] => none
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| d::ds => some (d, { eList := [], dList := ds })
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end Queue
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end Std
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